package com.wenhao.minglue;

import java.util.Scanner;

/**
 * @author Wenhao Tong
 * @create 2021-09-07 20:34
 */
public class Main1 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int a = 0;
        int b = 1;
        for (int i = 0;i <= n;i++) {
            a = a + b;
            b = a - b;
        }
        System.out.println(a);
    }
}
